The Mechanics Of A Breaking Pitch

Does a curveball really curve, or is it just an illusion? Finally, the definitive answer.

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It is Game 3 of the 1996 World Series. The Atlanta Braves have already taken the first two games in the Bronx. If they can beat the Yankees here in Fulton County Stadium, in Atlanta, they'll hold a seemingly insurmountable 3-0 lead in the Series and the Yankees can hang it up until next year.

But things have gone the Yankees' way in this game. A courageous effort by starting pitcher David Cone and excellent support by relievers Mariano Rivera and Graeme Lloyd have kept the Braves' big bats in check, and going into the bottom of the ninth, it's 5-2 Yankees as ace reliever John Wetteland takes the mound to close it out.

Wetteland is known for his blazing 99-mph fastball, and there is no reason for first batter Javier Lopez to look for anything else. Sure enough, Wetteland feeds Lopez nothing but heat and Lopez has all to do to ground feebly to Derek Jeter at short. But in his haste to make the play, Jeter bobbles the ball and Lopez is on.

Andrew Jones comes up. Jones, a rookie, has fed on Yankee pitching the first two games of the Series, including a couple of homers. A home run here and Atlanta is within one.

Wetteland bears down and brings heat. Jones looks at fastball after fastball, managing to foul a couple off and take a couple for balls. With the count two and two, Jones gears for yet another fastball as Wetteland comes set and checks the runner. At almost 100 mph, Wetteland's fastball reaches home plate in less than a second. Jones will have to start his swing before Wetteland actually releases the ball if he is to have any hope whatsoever of hitting it.

Wetteland deals. Jones starts his bat and begins to stride. The ball is released. But wait. Jones recognizes the spin on the ball. He sees the stitches. Oh no. Not a fastball. A breaking ball. Jones holds back his swing. His front leg has started to move. He holds back mightily. His left knee visibly buckles but he holds back. He can't pull the trigger. His only hope is that the pitch will be called a ball.

"Steeeeh!" screams plate umpire Tim Welke and Jones is out of there looking.

Strike three.

Such is the power of the unexpected breaking pitch in baseball, especially when a power pitcher like John Wetteland sets it up with one fastball after another. In fact, in this game the next batter, Jeff Blauser, strikes out on three straight fastballs and pinch-hitter Terry Pendleton grounds weakly to second to end the game. Knowing that Wetteland can throw a breaking ball at any moment is a weapon in itself. It throws off the batter's timing and prevents a hitter from merely sitting on a pitcher's fastball.

The breaking pitch–curveball, split-finger, slurve, slider and other variations–has been around since baseball began. But never have so many pitchers thrown so many different breaking pitches with so many different looks as today. Pity the poor batter who has to decide what he's going to do with any given pitch in the less than 1 second that it takes for the ball to leave the pitcher's hand and reach the hitting zone.

At one time, a batter could look for a fastball but was able to adjust to a breaking pitch that started out wide of the strike zone and then broke over, or a breaking pitch that started high of the strike zone and broke down into it. Today, most breaking pitches only move an inch or two within the strike zone. And that's all it takes to cause a batter to miss or to hit the ball feebly. And today, breaking pitches move left, right, down, diagonally and with variations on all of the above.

For years, the questions were whether a breaking pitch actually curved or whether it was just an optical illusion, or even simply a matter of trajectory. But now, with the availability of a laser-based, computerized optical system such as Supervision (see sidebar), it has been proven that the ball actually changes its flight path on the way to home plate.

As a former Major League pitcher myself, I threw thousands of breaking balls in my career. Frankly, I don't know why any one of them curved as it left my hand. I'll leave the physics of it to others with that type of expertise. What I can tell you is that I can make a ball curve, slide, break or drop. Much of the movement of the ball is controlled by the way it is gripped and released.

Breaking pitches spin, which results from applying finger pressure to the ball and snapping your wrist when releasing it. You'll get maximum spin by gripping the ball deeply within the fingers so that they wrap entirely around the ball, but your thumb has to be relaxed. I had an exercise I did when I was coaching pitchers. I'd say, "Squeeze the ball as tight as you can with your thumb and move your wrist." It didn't move very easily. But if you curl your fingers around the ball and barely lay your thumb on it, your entire wrist loosens up so you can snap it to get maximum spin.

The other element in a fast breaking pitch, such as a slider, is velocity. The key here is to stay behind the ball until the last possible second. Then, apply the wrist action for the particular pitch you're throwing. If you start rotating your wrist too early in the pitch, you lose velocity and get a slower, sloppier spin.

While no two hurlers have exactly the same style of pitching, all of them strive for a consistent delivery in terms of arm angle and release point. The batter draws an imaginary rectangular box right where the pitcher releases the ball, and he looks for clues in that area as to what type of pitch will be coming at him. If the pitcher drops his arm a bit when he delivers a curveball, for instance, the batter will pick up on this and know when to expect a curve. Snapping the wrist on the release should happen so quickly that the batter can't pick it up early in the delivery. Good hitters say they can recognize the curveball when it gets a particular distance from home plate. I think they overestimate their ability to pick up the spin. It happens so fast that they can't really see it until the ball gets close to home plate. They used to say Ted Williams could pick up a pitch right out of the hand. I don't know about that. I don't think anyone can pick it up that quickly.

Supervision Settles It

Pitchers, batters and catchers have always known that a breaking ball actually moves-that is, curves or sinks. But skeptics have maintained that the breaking ball is some kind of illusion. Supervision has settled the matter once and for all.

A 90-mph fastball takes four-tenths of a second to reach home plate. Supervision captures images of the pitch from 16 different locations in 3-dimensional positions using stadium-mounted cameras, computers, special-effects generators and trigonometric triangulation. The system can replay a graphic trajectory of the pitch within 1 second after the ball hits the catcher's mitt. It shows the ball's actual path of travel from mound to plate and breaking movement of the ball inside the strike zone.

It's a view batters wish that they could see before the pitch is thrown.

Looking at specific breaking pitches, the 2-seam fastball, also called a moving or sinking fastball, is gripped on top of the ball with the narrow seams exposed. This is in contrast to the 4-seam fastball, which must be gripped on the wide seams to get it to travel in a true trajectory with all seams rotating. Both of these fastball pitches are released with backspin.

When releasing this fastball, you usually apply pressure against the seam with either the index or middle finger. It's a matter of preference. This imparts the sidespin that causes the ball to drop. Lefthand pitchers like to use this pitch against lefthand hitters because the ball tends to break down and away.

Curveball

Years ago, this pitch was called a drop. I throw a curve with a 12 to 6 o'clock rotation. This release imparts sidespin and backspin because I maintain pressure on the ball with my middle finger while rolling it out over the top of my index finger. I like to throw the ball into the wind, because this increases the ball's rotation and helps the break. The key to the curveball is to keep your hand behind the ball as long as possible, impart the spin with the wrist and not with the elbow, and make sure the thumb is relaxed. I shorten my stride by 1 in. or so, compared to pitching a fastball. The object here is not to be throwing the ball toward the batter. You want a feeling like you're pulling down on the ball, almost like you're throwing it into the ground. This type of motion gives the ball the desired trajectory.

The screwball is actually the opposite of the curveball, in terms of snapping the wrist. Whereas I grip and release the ball with my palm turned inward for a curve, I turn my palm out when throwing a screwball–almost like I'm turning a screwdriver.

The ball's trajectory is similar to a curve, but it can't be thrown quite as hard. So the velocity is less than that of the curveball. Also, the ball breaks outward, instead of inward like a curveball. Lefthand pitchers like to throw screwballs to righthand hitters because the ball starts toward the middle of the plate and then breaks away to the outside corner.

The forkball, also known as a splitter or split-finger fastball, is an interesting pitch. You jam the ball between your first two fingers as hard as you can and deliver it with the same action as a fastball, with the wrist coming straight over from 12 to 6 o'clock. The ball travels with a lot of velocity, but with a tumbling kind of rotation. The rotation slows down as the ball approaches the plate, and if delivered correctly, the bottom kind of falls out of it.

The hard slider or short curve, as I used to call it, has a certain amount of lateral break and a certain amount of down break. It's a faster pitch than a curve but it's slower than a fastball, and it has a shorter break than a curveball. If you judged the pitch by miles per hour, and a pitcher's fast ball is, say, 90 mph, and his curveball is 80 mph, he would want the slider to be in the 86- to 87-mph range. The harder you throw a slider, the shorter and quicker the break you can get on it. The release technique is between a curve and a fastball.

Some pitchers release the ball off their middle finger. I throw my slider off my index finger. I try to feel like I'm wiping over the outside of the ball as I snap it, in order to give it some backspin and sidespin.

Other variations

Also, a lot of pitchers today throw a slurve. They pitch the slider as if they are throwing a curve, and the ball comes out in a big, sweeping flat curve. I consider this pitch to be just a rather sloppy slider. It has a much wider break than the slider was intended to have, and I think this is one of the reasons why there are so many more home runs today than 10 years ago. Pitchers like Tom Seaver could throw a true slider, whereas pitchers today would call that a cut fastball. A true slider breaks late and moves maybe 3 or 4 in.–sort of a little slide. A true slider should be more of a power pitch. Pitchers today use the slider more for a breaking ball or an off-speed pitch.

Of all my pitches, the one that brings up the fondest memories is the slider. I remember a game in the late '60s when I threw a real hard slider down and away to strike out Carl Yastremski to end the game with two men on. Striking out Carl was pretty hard to do. I remember seeing that ball break. I threw a similar pitch to Don Zimmer in '65 when I was playing for the Minnesota Twins, for the last out of the game against the Washington Senators to clinch the pennant. When the ball comes out of your hand, you can almost feel whether it's going to have a good break or a little slip to it. Both of those balls felt real crisp coming out, and they both broke in the same spot. I still remember them distinctly. I wonder if Yastremski and Zim do?

For years, many scientists believed that the curveball was an optical illusion. As we shall see, this is not true. In fact, physicists have long been aware of the fact that a spinning ball curves in flight, going back to Isaac Newton, who wrote a paper on the subject in 1671. In 1852, the German physicist Gustav Magnus revived the topic when he demonstrated in an experiment that when a spinning object moves through a fluid it experiences a sideways force. This phenomenon, now known as the Magnus Effect, is the fundamental principle behind the curved flight of any spinning ball.

The theory of the Magnus Effect is a relatively simple exercise in aerodynamics. When any object is moving through the air, its surface interacts with a thin layer of air known as the boundary layer. In the case of a sphere, which has a very poor aerodynamic shape, the air in the boundary layer peels away from the surface, creating a "wake" or low-pressure region behind the ball. The front-to-back pressure difference creates a backward force on the ball, which slows its forward motion. This is the normal air resistance, or aerodynamic drag, that acts on any object moving through the air. However, if the sphere is spinning as it moves, the boundary layer separates at different points on opposite sides of the ball–further upstream on the side of the ball that is turning into the airflow, and further downstream on the side of the ball turning backward. As a consequence, the air flowing around the ball is deflected slightly sideways, resulting in an asymmetrical wake behind the ball. The effect is to generate a pressure difference across the ball, creating a lateral force component that pushes the ball sideways. This lateral force, at right angles to the forward motion of the ball, is known as the Magnus force.

The strength of the Magnus force is in direct proportion to the rate of spin as well as the forward speed of the ball–the greater the forward speed, the greater the force. It will also be proportional to the air density, which means that a ball will tend to curve less at higher altitudes where the air is thinner–a boon to hitters in a high-altitude city like Denver. The stitches on the baseball also help to increase the Magnus force–not only by increasing the thickness of the boundary layer, but also by providing a place for the pitcher to put his fingers so that he can put more spin on the ball. It should be noted, however, that stitches are not required to make a ball curve. Even a smooth-surfaced table tennis ball will curve if it is given enough spin.

On the other hand, the direction of the Magnus force depends only on the direction of spin. As shown in the diagram, the force is always directed toward the side of the ball that is turning backward. In other words, the Magnus force always points in the same direction that the front of the ball is turning toward.

By properly orienting the spin direction, a pitcher can make the Magnus force point in any direction–left, right, up, down and so on. For example, the natural clockwise rotation of a righthander's wrist creates a leftward force (from the pitcher's perspective), which causes the ball to curve away from a righthand batter. When thrown with a three-quarters overhand motion, the same pitch will curve down and away from the batter. Conversely, a lefthand pitcher's natural wrist rotation (which is counterclockwise) causes the ball to curve left to right–that is, into a righthand batter and away from a lefthander. In order for a righthand pitcher to imitate this motion of throwing the pitch known as a screwball, he must turn his wrist counterclockwise as he releases the ball–an unnatural, uncomfortable motion that frequently leads to elbow trouble. Much of the strategy of baseball is a direct consequence of the fact that righthanders and lefthanders throw different pitches, simply because of the quirk of human physiology that our hands rotate more easily in one direction than the other.

A ball can be made to curve in a vertical plane as well. In fact, the trajectory of any thrown pitch has a natural downward curvature due to the force of gravity. However, by changing the spin direction, a pitcher can increase or decrease the curvature. For example, when a ball is thrown with a topspin, the Magnus force will act toward the ground, causing it to curve more sharply. If the ball is thrown with a backspin, the Magnus force will point away from the ground, causing the ball to curve less. The latter pitch produces what is often called a rising fastball. However, the laws of aerodynamics tell us that for a baseball to physically rise (that is, curve upward) as it approaches the batter, the Magnus force would have to be greater than the weight of the ball, and the rate of spin required to generate this much force is far beyond the ability of any pitcher. Thus, the rising fastball is an optical illusion. The baseball simply falls less than the batter expects it to.

It seems pretty clear that no right-minded physicist would ever argue that a curveball is an illusion. However, as with the case of the rising fastball, we will argue that the sharp break of a curveball is illusory. While many hitters often report that a good overhand curveball breaks so sharply that it looks like it is falling off a table, the laws of aerodynamics clearly show that the Magnus force cannot suddenly increase in flight–as would be required for a sudden change in curvature–but can only get smaller as the spin and speed of the ball slow down. The explanation for this illusion has to do with how the batter perceives the flight of the ball. The angular motion of the ball–that is, its apparent motion across the batter's field of vision–seems relatively slow at first, but then increases rapidly as the ball approaches. In fact, it has been demonstrated that the angular motion becomes so rapid that no batter could possibly move his head fast enough to keep his eye on the ball all the way. When a good curveball is thrown, the change in its angular motion becomes even more pronounced as it nears the batter, greatly enhancing the appearance of its natural curvature and giving the illusion of a sharp bend.